{Ca(OH₂)₃[Ca(DOTA)].7.7H₂O}_n

The octadentate ligand H₄DOTA (H₄DOTA = 1,4,7,10-tetraazacyclododecane-N,N',N",N′′′-tetraacetic acid) forms the most stable calcium complexes known. The overall solid state structure of the title complex {poly[triaqua-μ-(1,4,7,10-tetraazacyclododecane)-N,N',N",N′′′-tetraacetato)-dicalcium 7.7-hydrate], [Ca₂(C₁₆H₂₄N₄O₈)(H₂O)₃].7.7H₂O} contains two independent eight-coordinate Ca²⁺ ions on a twofold crystallographic axis with the Ca²⁺ ions bound to four of the eight O atoms [mean Ca-O = 2.45 (3) Å] and the four N atoms [mean Ca-N = 2.59 (2) Å] of the DOTA ligand. The coordination geometry of the Ca atom encapsulated by the DOTA ligand is distorted square antiprismatic. Carboxylate bridges link [Ca(DOTA)]²⁻ anions to [Ca(OH₂)₃]²⁺ counterions (on general positions related by the twofold symmetry) to form a neutral tetranuclear unit, which in turn bridges to surrounding units through a carboxylate O atom and generates a one-dimensional chain.

-1